Many commercial, industrial, and government facilities, indoor as well as outdoor, require a significant number of lighting fixtures for adequate illumination, and therefore use a significant amount of power to operate the fixtures. To reduce the power to light these facilities, as well as the cost of maintaining them (e.g., replacing bulbs), a number of facilities use high intensity discharge (HID) light sources including metal halide (MH) and high pressure sodium (HPS) lamps, as well as other discharge lamps, in lieu of incandescent lamps.
Although use of discharge lamps alone can reduce power consumption as compared to incandescent lamps, energy consumption can be further reduced by dimming systems which control when and the level to which these discharge lamps are energized. For example, step-dimming systems, such as two-level or high-low lighting control systems, can be used to switch facility fixtures between energy-saving low level or reduced-wattage operation and full level or normal-wattage operation. Thus, light fixtures, for example, in office buildings, prisons, warehouses, convention centers, stadiums, tunnels, roadways, parking facilities and the like can be dimmed or illuminated to normal-wattage operation automatically in accordance with occupancy level, ambient light level, time, and manual switching, among other conditions. Step-dimming systems can therefore reduce energy consumption, increase security and/or provide multi-function lighting levels.
U.S. Pat. No. 5,216,333 to Nuckolls et al., which is hereby incorporated herein by reference in its entirety, discloses a step-dimming magnetic regulator which increases or reduces light output from a discharge lamp in accordance with the output signals from a motion sensor. As shown in the attached FIG. 1, a magnetic regulator 10 comprises a primary winding 12, the line wire L and neutral wire N of which are connected to an AC power source. The regulator also comprises a secondary winding 14 and a tertiary winding 16 magnetically coupled, together with the primary winding, by a laminated core 18. The secondary winding 14 has a tap 15 connected to a starting circuit 21 for providing high voltage pulses to the discharge lamp 22. The tertiary winding 16 is the capacitance winding of the regulator 10. A capacitor 24 is connected between the ends of the tertiary winding. The winding 16 is also provided with a tap 26 which is used to operate a dimming reactor 30.
With continued reference to FIG. 1, the reactor 30 is connected in series with a switchable conductive path comprising a normally closed contact set 32 between one end of the winding 16 and the center tap 26. An electromagnetic actuator, e.g., a relay winding 28, opens the contact set 32 when a switch 34 is actuated. The switch 34 can be, for example, an infrared (IR) sensor which reduces its internal resistance to near zero when a condition, such as a human body moving within its area of sensitivity. The switch 34 is connected between the neutral wire N and the relay winding 28 by single control wire 44. When the switch 34 is actuated, relay 28 is connected between a center tap 13 on the primary winding and the neutral wire N via the control wire 44. When the wire 44 is connected to neutral, the relay 28 is energized and therefore opens the contact set 32. When the contact set 32 is open, the reactor 30 has no effect on circuit operation. When the contact set 32 is closed, the reactor 30 extracts positive volt-amperes and stores that energy each half-cycle, thereby reducing the amount of energy stored by capacitor 24 for operating the lamp. The lamp is therefore dimmed. A plurality of lamp and dimmer units 40a, 40b can be connected to the same switch by a single wire.
With reference to FIG. 2, the Nuckolls U.S. Pat. No. 5,216,333 further discloses an arrangement of sensors 67 and 68 and regulator and lamp units 66 in a room or aisle 64. The units 66 comprise the regulator, lamp dimming reactor and switchable conductive path discussed in connection with FIG. 1. When motion is sensed by either sensor 67 or 68, the dimming reactors are removed from the circuit, allowing light output from all of the lamps to be increased promptly. More specifically, a power supply 72 supplies a low DC voltage to each of the motion sensors 67 and 68. The output of the sensors 67 and 68 are connected to relays 74 and 75, respectively. The relays 74 and 75 have normally open contact sets 76 and 77, respectively, which close when the relays are energized. The lamp units 66 has an internal relay and control wire similar to the relay 28 and control wire 44 described in connection with FIG. 1. When either sensor detects motion, relay 74 or 75 closes its contact set, connecting the control wire for all fixtures to neutral. Thus, the internal relay in each lamp is energized to remove its internal ballast and increase lamp output.
With reference to FIG. 3, another lighting control system manufactured by Ruud Lighting, Inc. of Racine, Wash. for providing two level (i.e., high-low) lighting comprises an internal switching device and a single control wire. The fixtures 80a, 80b and 80c receive power from a three-phase power source 82, and the voltage supplied thereby is phase-to-neutral or ground. A control module 84 receives power from a power pack 86 and comprises a sensor 88 (e.g., a passive infrared occupancy sensor) and a manual override switch 90. When a human body is detected by the sensor 88, or the switch 90 is closed, a contact set (not shown) within the control module connects the single control wire 92 leading to the fixtures to the voltage potential.
The lighting system in the Nuckolls U.S. Pat. No. 5,216,333 and the Ruud lighting system are disadvantageous for a number of reasons. For example, the Ruud system switches to a line voltage, which is not as safe as switching to neutral. The Nuckolls patent is disadvantageous because it uses a reactor (e.g., reactor 30 in FIG. 1) which increases the size and cost of the control system.